Pivot mounting for oscillatory tool



P 5, 1966 E. G. STURGEON PIVOT MOUNTING FOR OSCILLATORY TOOL 5 Sheets-Sheet 1 Filed Nov. 14, 1965 Sept. 6, 1966 E. G. STURGEON 3,271,598

PIVOT MOUNTING FOR OSCILLATORY TOOL Filed NOV. 14. 1963 3 Sheets-Sheet 2 INVENTOR. i Zwdrifi 52277 90021 aim/17m PL 6, 1966 E. G. STURGEON 3,271,598

PIVOT MOUNTING FOR OSGILLATORY TOOL Filed NOV. 14, 1963 5 Sheets-Sheet 5 E lfi. INVENTOR.

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United States Patent 3,271,598 PIVOT MOUNTING FOR OSCILLATORY TOOL Edward G. Sturgeon, Orchard Lake, Mich., assignor to Syncro Corporation, Oxford, Mich, a corporation of Michigan Filed Nov. 14, 1963, Ser. No. 323,678 7 Claims. (Cl. 310-49) This invention relates to oscillatory tools, and more particularly to means for pivotally mounting the armatures and connected tool holders of electromagnetically operated oscillatory sanders or the like.

It is an object of the present invention to provide an armature support for an electromagnetic reciprocating tool motor which is an improvement over that shown and claimed in Patent No. 2,836,940, issued to Thomas F. Carmichael on June 3, 1958. It has been found that the armature support shown in that patent restricts the length of stroke which is feasible with portable sanders or the like in that one or more of the support rods will sometimes fail by breakage after a relatively short period of use if the stroke is greater than a certain amount. Sometimes a single rod may break in an armature support made according to the aforementioned patent, but the break remains undetected, the remaining rods taking the entire load. In such cases, however, the pivoting action will be off center, decreasing the efliciency of the tool and sometimes tending to raise the noise level.

An object of the present invention is to provide an armature support which includes all the important advantages of that shown in the aforementioned patent but in which none of the rods will fail even after extended use with a relatively long stroke.

These and other objects of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings.

In the drawings:

FIGURE 1 is a side elevational view of an electromagnetic motor for a portable sander showing the novel armature support;

FIG. 2 is a top plan view of the motor;

FIG. 3 is an end elevational view taken in the direction of the arrow 3 of FIGURE 1;

FIG. 4 is an end elevational view taken in the direction of the arrow 4 of FIGURE 1;

FIG. 5 is a fragmentary cross-sectional view taken along the line 5-5 of FIG. 2;

FIG. 6 is an exaggerated side elevational view of a portion of a single rod shown in its unstretched condition;

FIG. 7 is an end elevational view of the unstretched rod taken in the direction of the arrow 7 of FIG. 6;

FIG. 8 is a view similar to FIG. 6 but showing the rod in its stretched condition; and

FIG. 9 is a view of the rod taken in the direction of the arrow 9 of FIG. 8.

Briefly, the illustrated embodiment of the invention comprises an electromagnetic motor having a core on which a coil is mounted, and an armature mounted adjacent the core and carrying a platen for a portable sander. The core has a pair of spaced securing legs at one end which are on opposite sides of a portion of the armature and spaced therefrom. The armature has an apertured portion through which extend a group of springlike rods arranged in annular fashion, the rods extending from opposite ends of the armature aperture into apertures formed in the core legs. Plugs are forced into the spaces formed by the rods within the armature and core apertures, frictionally securing the rods in position. The diameter of the apertures in the core legs is slightly greater than the diameter of the aperture in the armature, so that the rods flare outwardly in a slightly curved or S-shaped fashion as they extend from the armature to the core legs. Because of this curvature, sufficient slack exists in the rods to permit a relatively long armature stroke during operation of the motor, the slack being taken up at the opposite ends of the stroke, thus preventing excessive stresses in the rods which might result in slippage at their connections with the core legs or in fatigue failure after continued use.

Referring more particularly to the drawings, the electromagnetic reciprocating motor is generally indicated at 11 and comprises an armature 12 and a core 13, these elements being fabricated in laminar fashion. Core 13 is of generally E-shaped construction, having a coil 14 mounted on the central portion thereof. A pair of armature supporting brackets or legs 15 and 16 are secured to one end of core 13 and extend outwardly on opposite sides of armature 12, as seen in FIG. 3.

The armature is of generally L-shaped construction, its main portion extending past coil 14, as seen in FIG. 2, and having an extension 17 (FIG. 5) within the coil. The shorter leg of the armature is disposed between the outwardly projecting ends of legs 15 and 16, as seen in FIGURE 3. The armature carries a bracket 18 extending to one side thereof, and a platen 19 is secured to a pair of legs 21 and 22 at the lower end of bracket 18, as seen in FIGS. 1 and 2. A pair of helical coil compression springs 23 and 24 are disposed between the core and armature, as seen in FIGS. 3 and 4, the core carrying L-shaped brackets 25 and 26 which support springs 23 and 24, respectively, and are secured to the end of the core opposite that which carries legs 15 and 16. A pair of brackets 27 and 28 are secured to armature 13 and support the other ends of springs 23 and 24, respectively. Springs 23 and 24 tend to urge the armature away from the core, the pulsating flux created by current within coil 14 coacting with the springs to create rapid reciprocating movement of armature 12 during operation of the tool.

The portion of armature 12 between brackets 15 and 16 is provided with an apertured portion 29, as seen in FIGS. 6 and 8, this apertured portion having flared upper and lower ends 31. Brackets 15 and 16 are provided with apertured portions 32, the diameter of apertured portions 32 being slightly greater than the diameter of aperture 29. This difference in diameters is exaggerated in FIGS. 6 and 8 to aid understanding of the invention.

A plurality of circumferentially arranged rods 33 are disposed within apertured portions 29 and 32, the rods extending axially the entire distance between the upper surface of bracket 15 and the lower surface of bracket 16. These rods are fabricated of an appropriate metal having spring-like qualities and together form an annular arrangement as seen in FIG. 2. The lengths of the rods are identical, this length being such that when the rods are in their normal centered position, as seen in FIGS. 6 and 7, they will have a substantial amount of slack or extra length between upper apertured portion 32 and apertured portion 29, and between lower apertured portion 32 and apertured portion 29, the latter portion of the rod not being seen in FIGS. 6 to 9.

The rods are frictionally secured to armature 12 by a plug 34 which is tape-red at both ends and is forced into the space surrounded by the rods, plug 34 thus forcing the rods outwardly against apertured portion 29. The length of plug 34 may be slightly less than the total length of apertured portion 29, including its flared ends 31. The upper and lower ends of the rods are fixed to legs 15 and 16 by plugs 35 and 36, respectively, as seen in FIG. 3. These plugs are tapered at their inwardly facing ends and are slightly longer than the length of apertured portions 32. They likewise force rods 33 outwardly, causing them to be in firm frictional engagement with legs 15 and 16. Because of the fact that the diameter of apertured portions 32 is slightly greater than that of apertured portion 29, the upper and lower ends of the rods will be slightly spaced apart in a circumferential direction, whereas the central portions of the rods within apertured portions 29 may be in contact with each other. The spacing of the upper and lower ends of the rods is not shown in FIG. 2 because it is so slight.

In operation, armature 12 will vibrate back and forth (clockwise and counterclockwise) from its FIG. 2 position in response to pulsating flux created by cur-rent passing through coil 14, and the action of springs 23 and 24. During this rapid reciprocation about a pivotal axis passing through the centers of plugs 34 and 35, the free portions of rods 33 will be slightly twisted in alternately opposite directions, the twisting action being a combined motion including a twisting movement about each rods own axis, plus an angular bending with respect to the axis of plugs 34 and 35.

FIGS. 6 to 9 illustrate the action of a single rod 33 in order to bring out more clearly the advantages of the invention. FIGS. 6 and 7 show the rod in an intermediate or unstretched position, that is, a position between its two extreme positions of oscillation. It will be noted that the slack in rod 33, which is exaggerated in FIGS. 6 and 7 for purposes of clarity, will create a slightly S-shaped configuration of the free portion of each rod. Actually, because of the spring-like nature of the rods, they will tend to elongate when in the position of FIGS. 6 and 7, that is, they will have a tendency to straighten themselves out, but will beprevented'from doing so by the fact that they are fixed to legs and 16 which in turn are a fixed distance from each other. The weight of armature 12 and its attached parts, which in theory would tend to straighten the upper free length of rods 33 and increase the curvature of the lower free length, and upward forces on the armature when sanding which would have the opposite tendency, may be disregarded for purposes of this explanation, since these forces will be negligible compared with the other forces acting on rods 33.

As armature 12 moves from its central position in one direction or the other, the movement of each rod 33, described above, will cause the slack in the free portions of the rod to be taken up, either partially or completely, so that the S shape will be flattened or will disappear altogether. This is illustrated in FIGS. 8 and 9, wherein it will be seen that the portions 31 of apertured portion 29 will permit this flattening to take place without interference.

As the armature moves back from each extreme end end its stroke toward its central position, the S shape in each rod 33 will reappear and will increase until the central point is passed, after which it will again decrease as the armature moves toward the other extreme end of its stroke. I

The result will be that the upper and lower ends of rods 33, which are secured between plugs 35 and legs 15 and 16, respectively, will not tend to be pulled toward each other. There will also be no substantial axial tensile force created in rods 33. It has been found that with this construction, the useful life of the pivot mounting is greatly increased and that a longer are of stroke is possible for the armature during this life without the danger of fatigue failure of one or more rods 33.

While it will be apparent that the preferred embodiment herein illustrated is well calculated to fulfill the objects above stated, it will be appreciated that the invention is susceptible to modification, variation and change Without departing from the proper scope or fair meaning of the subjoined claims.

What is claimed is:

1. In a mount for pivoting a first part relative to a second part in an electromechanical vibrator, an apertured portion in said first part, an apertured portion in said second part slightly larger in diameter than said first apertured portion, said apertured portions being in concentric but axially spaced relation, and a plurality of annularly arranged spring-like rods disposed within said apertured portions and extending therebetween, the portions of said rods within said apertured portions being fixed thereto, the portions of said rods between the apertured portions having some slack so as to form a slight S-shape, whereby reciprocation of said first part relative to said second part about the common axis of said concentric apertured portions will cause the slack in said rods to be at least partially taken up as the extreme end of each arcuate stroke is reached.

2. In a pivotal mounting for a first part which is movable relative to a second part in an electromechanical vibrator, a pair of legs on said second part disposed on opposite sides of and spaced from a portion of said first part, apertured portions in said legs and said first part portion, said apertured portions being in concentric relation but with the apertured portion of said first part having a slightly smaller diameter than the apertured portions of said legs, a group of annularly arranged spring-like rods extending through said apertured portions, and means for securing the portions of said rods within said apertured portions of said legs and first part, respectivley, the free lengths of said rods between said apertured portions having some slack so as to form a slight S-shape when the first part is in a central angular position with respect to said second part, arcuate movement of said first part with respect to said second part about the pivot created by said rods causing the free lengths of said rods to stretch and tend to become taut, thus flattening said S-shapes.

3. The combination according to claim 2, said means for fixing said rods within said apertured portions comprising plugs forced into the spaces surrounded by said rods.

4. In a pivot mounting for the armature of a reciprocating electromagnetic motor having an armature member, core member, and coil mounted on said core member, apertured portions on said members, said apertured portions being concentric but in axially spaced relation, one of said apertured portions being slightly larger in diameter than the other, a plurality of annularly arranged spring-like rods extending between and into said apertured portions, and means securing said rods in said apertured portions, the free portions of said rods between said apertured portions having some slack and being slightly S-shaped in their unstretched position when said armature is in a central position with respect to its arcuate stroke, movement of the armature toward either end of its arcuate stroke causing said free portions of the rods to take up said slack.

5. In a pivot mounting for the armature of an electromagnetic reciprocating motor having an elongated armature, E-shaped core, and coil mounted on the central portion of said core, a pair of legs on one end of said core, said legs being spaced from and on opposite sides of one end of said armature, said legs and the armature portion between the legs having apertured portions, the apertured portion in said armature being of slightly smaller diameter than the apertured portions in said legs, spring means between said armature and core urging the armature away from the core, a plurality of springlike rods of circular cross-sectional shape extending through said apertured portions and between said armature and legs, said rods being annularly arranged and in closely adjacent relation within the apertured portion of said armature, and plugs within said apertured portions forcing the portions of said rods within said apertured portions against the walls of the apertured port1ons so as to be in frictional contact therewith, the free lengths of said rods between said apertured portions having some slack and being slightly S-shaped in their unstretched condition w=hen the armature is at rest, at least some of the slack of said free rod lengths being taken 5 up when said armature approaches each end of its arcuate stroke.

6. The combination according to claim 5, said plugs being tapered to facilitate their being forced into the space surrounded by said rods, and relieved portions at the ends of said armature apertured portions to provide clearance for the movement of said free rod lengths.

7. In a pivot mounting for the armature of a reciprocating electromagnetic motor having an armature member, core member, and coil mounted on said core member, a pair of legs on one of said members, said legs being spaced from and on opposite sides of said other member, an apertured portion in said other member, a pair of apertured portions in said legs axially aligned with said first apertured portion but of slightly larger diameter, a plurality of spring-like rods of circular crosssectional shape extending through said apertured portions, said rods being annularly arranged and in closely adjacent relation within the apertured portion of said other member, the ends of said rods being annularly arranged within the apertured portions of said legs, and plugs Within said apertured portions forcing the portions of said rods Within the apertured portions against the walls of the apertured port-ions so as to be in frictional contact therewith, the free lengths of said rods between said apertured portions having some slack and being slightly S-shaped in their unstretched condition when the armature member is at rest, at least some of the slack of said free rod lengths being taken up when said armature member approaches each end of its arcuate stroke.

References Cited by the Examiner UNITED STATES PATENTS 2,836,940 6/1958 Carmichael 310-38 X 3,053,965 9/1962 Kintzel 31015 X 3,170,078 2/1965 Kuschel 31029 MILTON O. HIRSHFIELD, Primary Examiner.

D. F. DUGGAN, Assistant Examiner. 

5. IN A PIVOT MOUNTING FOR THE ARMATURE OF AN ELECTROMAGNETIC RECIPROCATING MOTOR HAVING AN ELONGATED ARMATURE, E-SHAPED CORE, AND COIL MOUNTED ON ONE END OF SAID PORTION OF SAID CORE, A PAIR OF LEGS ON ONE END OF SAID CORE, SAID LEGS BEING SPACED FROM AND ON OPPOSITE SIDES OF ONE END OF SAID ARMATURE, SAID LEGS AND THE ARMATURE PORTION BETWEEN THE LEGS HAVING APERTURE PORTIONS, THE APERTURE PORTION IN SAID ARMATURE BEING OF SLIGHTLY SMALLER DIAMETER THAN SAID ARMATURE BEING OF SLIGHTLY SPRING MEANS BETWEEN SAID ARMATURE AND CORE URGING THE ARMATURE AWAY FROM THE CORE, A PLURALITY OF SPRING LIKE RODS OF CIRCULAR CROSS-SECTIONAL SHAPE EXTENDING THROUGH SAID APERTURED PORTIONS AND BETWEEN SAID ARMATURE AND LEGS, SAID RODS BEING ANNULARLY ARRANGED AND IN CLOSELY ADJACENT RELATION WITHIN THE APERTURED PORTION OF SAID ARMATURE, AND PLUGS WITHIN SAID APERTURED PORTIONS FORCING THE PORTIONS OF SAID RODS WITHIN SAID APERTURED PORTIONS OF SAID RODS WITHN SAID APERTIONS SO AS TO BE IN FRICTIONAL CONTACT THEREWITH, THE FREE LENGTHS OF SAID RODS BETWEEN SAID APERTURED PORTIONS HAVING SOME SLACK AND BEING SLIGHTLY S-SHAPED IN THEIR UNSTRETCHED CONDITION WHEN THE ARMATURE IS AT REST, AT LEAST SOME OF THE SLACK OF SAID FREE ROD LENGTHS BEING TAKEN UP WHEN SAID ARMATURE APPROACHES EACH OF ITS ARCUATE STROKE. 